Background: From 2000 a routine survey of mothers with newborn infants was commenced in South Western Sydney. The survey included the Edinburgh Postnatal Depression Scale (EPDS). The aim of the study was to determine the prevalence and risk factors for postnatal depressive symptoms in women living in metropolitan Sydney, Australia. Methods: Mothers (n=15,389) delivering in 2002 and 2003 were assessed at 2–3 weeks after delivery for risk factors for depressive symptoms. The binary outcome variables were EPDS >9 and >12. Logistic regression was used for the multivariate analysis. Results: The prevalence of EPDS >9 was 16.93 per 100 (95% CI: 16.34 to 17.52) and EPDS >12 was 7.73 per 100 (95% CI: 6.96 to 7.78). The final parsimonious logistic regression models included measures of infant behaviour, financial stress, mother’s expectation of motherhood, emotional support, sole parenthood, social support and mother’s country of birth. Conclusions: Infant temperament and unmet maternal expectations have a strong association with depressive symptoms with implications for the design of both preventative and treatment strategies. The findings also support the proposition that social exclusion and social isolation are important determinants of maternal depression.